The present invention relates to the art of sand blasting and more particularly to an improved spin blast tool resistant to internal abrasion.
Metal work pieces, such as pipe and castings, require sand blasting for cleaning and treatment. Sand blasting includes projecting a blast or stream of sand and air under pressure onto the metal work piece so that the sand and air mixture impinges on the work piece. The pressurized air and sand abrades and thus cleans the surface of the metal. Sand blast tools generally include a nozzle which directs the pressurized mixture of sand and air onto the surface of the work piece.
It is preferred that the stream of air and sand from the nozzle of the spin blast tool be maintained in motion over the metal surface to be cleaned in order to accomplish a uniform effect. Such spin blast tools are disclosed and described in U.S. Pat. Nos. 2,358,577; 2,724,928; and 3,137,974. Although a single nozzle may be used from which to direct the blast of sand and air toward the work piece, it is generally preferred for the spin blast tool to have a nozzle which provides two streams of air and sand under pressure from a single source to permit covering a larger area in less time than is possible with a single blast nozzle.
For example, U.S. Pat. No. 3,137,974 discloses a rotary cleaning device utilizing a continual swirling action for the abrasive sand to impinge on the work piece. The nozzle has a plurality of blast producing outlets by which the blast of sand emanating therefrom will provide a reactive force which will impart a swirling of the sand blast nozzle as the sand and air stream therefrom. This results in a more uniform distribution of the sand blast and thus avoids pitting and overblasting.
One of the deficiencies of the prior art tools is that not only does the sand abrade the metal of the work piece, it also abrades the interior of the spin blast tool. The spin blast tool is connected to a conduit which supplies the compressed air and sand for the spin blast tool. The interior of the tool is abraded as the air and sand passes through the tool and thereafter out through the nozzle. The passage of sand through the interior of the tool tends to pit, abrade, and otherwise deteriorate the tool, particularly the conduits and rotary connections within the tool. This abrasion causes spin blast tools to have a relatively short life and requires frequent replacement or repair due to the deterioration.
The prior art tools have seals to protect the rotary connections against the abrasive sand. However, these seals deteriorate so quickly that they have to be replaced within a matter of hours; plus, the abrasion and deterioration of the seals limit the usage and life of the sand blast tool.
The continual replacement of seals requires the expenditure of much time and money. Further, damage to the tool, such as the abrasion of rotary connections, may occur if such seals are not promptly replaced.
It is the object of the present invention to overcome this internal abrasion, to substantially extend the life of the metal parts of the tool, and to improve the seals and protection of the rotary connections of the tool. Other objects and advantages of the invention will be apparent from the following description.